Switch Statements

Signs and Symptoms

You have a complex switch operator or sequence of if statements.

Reasons for the Problem

Relatively rare use of switch and case operators is one of the hallmarks of object-oriented code. Often code for a single switch can be scattered in different places in the program. When a new condition is added, you have to find all the switch code and modify it.

As a rule of thumb, when you see switch you should think of polymorphism.

Treatment

• To isolate switch and put it in the right class, you may need Extract Method and then Move Method.

• If a switch is based on type code, such as when the program’s runtime mode is switched, use Replace Type Code with Subclasses or Replace Type Code with State/Strategy.

• After specifying the inheritance structure, use Replace Conditional with Polymorphism.

• If there aren’t too many conditions in the operator and they all call same method with different parameters, polymorphism will be superfluous. If this case, you can break that method into multiple smaller methods with Replace Parameter with Explicit Methods and change the switch accordingly.

• If one of the conditional options is null, use Introduce Null Object.

Payoff

• Improved code organization.

When to Ignore

• When a switch operator performs simple actions, there’s no reason to make code changes.

• Often switch operators are used by factory design patterns (Factory Method or Abstract Factory) to select a created class.